Proteins are used in a wide range of applications in the fields of industrial chemistry, pharmaceuticals, veterinary products, cosmetics and other consumer products, foods, feeds, diagnostics and decontamination. At times, such uses have been limited by constraints inherent in proteins themselves or imposed by the environment or media in which they are used. Such constraints may result in poor stability of the proteins, variability of performance or high cost. In order for proteins to realize their full potential in the fields in which they are used, they must be able to function without excessive intervention by their surrounding environment. In the past, environmental elements have often posed barriers to the widespread use of proteins.
Various approaches have been employed to overcome these barriers. However, these approaches have incurred either loss of protein activity or the additional expense of protein stabilizing carriers or formulations.
One unique approach to overcoming barriers to the widespread use of proteins is crosslinked enzyme crystal ("CLEC.TM.) technology [N. L. St. Clair and M. A. Navia, J. Am. Chem. Soc., 114, pp. 4314-16 (1992)]. Crosslinked enzyme crystals retain their activity in environments that are normally incompatible with enzyme function. Such environments include prolonged exposure to proteases and other protein digestion agents, high temperature or extreme pH. In such environments, crosslinked enzyme crystals remain insoluble and stable.
Protein solubility, leading to controlled release or dissolution of protein, is important in many industrial fields. Such industries include those concerning cleaning agents, including detergents, pharmaceuticals, consumer and personal care products, veterinary products, foods, feeds, diagnostics and decontamination. Various approaches to controlled release have been proposed. These include encapsulation, such as that described in U.S. Pat. Nos. 4,579,779 and 5,500,223. Other approaches include the use of mechanical or electrical feed devices and osmotic pumps.
Controlled release in the pharmaceutical field has been addressed by various means. U.S. Pat. No. 5,569,467 refers to the use of sustained release microparticles comprising a biocompatible polymer and a pharmaceutical agent, which is released as the polymer degrades. U.S. Pat. No. 5,603,956 refers to solid, slow release pharmaceutical dosage units comprising crosslinked amylase, alpha amylase and a pharmaceutical agent. U.S. Pat. No. 4,606,909 refers to oral, controlled-release multiple unit formulations in which homogeneous cores containing particles of sparingly soluble active ingredients are coated with a pH-sensitive erodable coating. U.S. Pat. No. 5,593,697 refers to pharmaceutical or veterinary implants comprising a biologically active material, an excipient comprising at least one water soluble material and at least one water insoluble material and a polymer film coating adapted to rupture at a predetermined period of time after implant.
The objective of controlled release of proteins, however, must be balanced with the fact that the protein itself may not be stable under storage conditions. Protein stability may also be adversely affected by other components of the formulation in which it is contained. For example, heavy duty liquid detergents constitute hostile environments for component enzymes. Such problems have been approached through the use of mutant subtilisin proteases, which are said to have improved oxidative stability. See U.S. Pat. No. 4,760,025 and PCT patent application WO89/06279. Proteins, the enzymes most widely used in detergents, catalyze their own decomposition. Strategies such as the addition of protease inhibitors (e.g., borate with glycols) or the lowering of water activity have been only partially effective.
Another approach, described in U.S. Pat. No. 5,385,959, is encapsulation of degradation-sensitive detergent components in capsules of composite emulsion polymers, which permit dilution release thereof. U.S. Pat. No. 5,286,404 refers to a liquid detergent composition said to have improved enzyme solubility while preserving enzyme activity. The improvement is attributed to chemical modification of free primary amino groups in an enzyme solution via aldehyde treatment, acylation or alkylation.
Despite such progress in protein technology generally, the need still exists for proteins which are stable under conditions of storage, while active under conditions of use.